Conventionally known are two-hand switch devices that can be operated only when both hands of a worker are placed in pre-determined safe positions so that a machine such as a press is prevented from activating when a hand of the worker is placed in a hazardous part. See Patent Document #1, for instance.
In the case of a press, a left hand safe position and a right hand safe position are designated some distance away from a work piece charge inlet of the press in a laterally spaced apart relationship. Each of the left and right hand safe positions is typically fitted with a push button switch having a relatively large button head. Only when both of the push button switches are depressed, a pre-determined signal is produced from the two-hand switch device. The output signal is used as a condition for activating a press stroke of the press, determining an activation timing of a press stroke and so on.
The right and left push button switches are adequately spaced apart from each other so that the two switches may not be depressed by using one hand, and are each fitted with a relatively strong return spring.
Therefore, when performing a press work by operating the two-hand switch device, the worker is required to place his right and left hands on the right and left push button heads, respectively, and forcibly depress the two push button switches. Thereby, the press stroke of the press is prevented from being initiated when a hand of the worker is placed in a hazardous part of the press.
In a sensor type press controller that involves a condition for activating the press based on the blocking of sensor light, it is conventionally known to fit a transmitter to each wrist of the worker and control the condition for activating the press for each different worker identified by an ID code transmitted from the corresponding transmitter.
[Patent Document #1]
Japanese patent laid open (kokai) publication No. 05-212597
[Patent Document #2]
Japanese patent laid open (kokai) publication No. 10-180495